Hydrothermally synthesized Mo-V-M-X oxide catalysts for the selective oxidation of hydrocarbons

ABSTRACT

Hydrothermally synthesized catalysts comprising a mixed metal oxide are utilized to produce unsaturated carboxylic acids by the vapor phase oxidation of an alkane, or a mixture of an alkane and an alkene, in the presence thereof; or to produce unsaturated nitriles by the vapor phase oxidation of an alkane, or a mixture of an alkane and an alkene, and ammonia in the presence thereof.

This non-provisional application is a divisional of non-provisional U.S.patent application Ser. No. 10/165,892 filed Jun. 10, 2002, now grantedas U.S. No. 6,746,983, benefit of which is claimed under 35 U.S.C. § 120and which in turn claims benefit under 35 U.S.C. § 119(e) of U.S.provisional Application No. 60/299,213, filed Jun. 18, 2001, prioritybenefit of which is also claimed for the present application.

The present invention relates to a catalyst for the oxidation ofalkanes, or a mixture of alkanes and alkenes, to their correspondingunsaturated carboxylic acids by vapor phase catalytic oxidation; to amethod for making the catalyst; and to a process for the vapor phasecatalytic oxidation of alkanes, or a mixture of alkanes and alkenes, totheir corresponding unsaturated carboxylic acids using the catalyst. Thepresent invention also relates to a process for the vapor phasecatalytic oxidation of alkanes, or a mixture of alkanes and alkenes, inthe presence of ammonia, to their corresponding unsaturated nitritesusing the catalyst.

Nitriles, such as acrylonitrile and methacrylonitrile, have beenindustrially produced as important intermediates for the preparation offibers, synthetic resins, synthetic rubbers, and the like. The mostpopular method for producing such nitrites is to subject an olefin suchas propene or isobutene to a gas phase catalytic reaction with ammoniaand oxygen in the presence of a catalyst at a high temperature. Knowncatalysts for conducting this reaction include a Mo—Bi—P—O catalyst, aV—Sb—O catalyst, an Sb—U—V—Ni—O catalyst, a Sb—Sn—O catalyst, aV—Sb—W—P—O catalyst and a catalyst obtained by mechanically mixing aV—Sb—W—O oxide and a Bi—Ce—Mo—W—O oxide. However, in view of the pricedifference between propane and propene or between isobutane andisobutene, attention has been drawn to the development of a method forproducing acrylonitrile or methacrylonitrile by an ammoxidation reactionwherein a lower alkane, such as propane or isobutane, is used as astarting material, and it is catalytically reacted with ammonia andoxygen in a gaseous phase in the presence of a catalyst.

In particular, U.S. Pat. No. 5,281,745 discloses a method for producingan unsaturated nitrile comprising subjecting an alkane and ammonia inthe gaseous state to catalytic oxidation in the presence of a catalystwhich satisfies the conditions:

(1) the mixed metal oxide catalyst is represented by the empiricalformulaMo_(a)V_(b)Te_(c)X_(x)O_(n)wherein X is at least one element selected from the group consisting ofniobium, tantalum, tungsten, titanium, aluminum, zirconium, chromium,manganese, iron, ruthenium, cobalt, rhodium, nickel, palladium,platinum, antimony, bismuth, boron and cerium and, when a=1, b=0.01 to1.0, c=0.01 to 1.0, x=0.01 to 1.0 and n is a number such that the totalvalency of the metal elements is satisfied; and

(2) the catalyst has X-ray diffraction peaks at the following angles(±0.3°) of 2θ in its X-ray diffraction pattern: 22.1°, 28.2°, 36.2°,45.2° and 50.0°.

Unsaturated carboxylic acids such as acrylic acid and methacrylic acidare industrially important as starting materials for various syntheticresins, coating materials and plasticizers. Commercially, the currentprocess for acrylic acid manufacture involves a two-step catalyticoxidation reaction starting with a propene feed. In the first stage,propene is converted to acrolein over a modified bismuth molybdatecatalyst. In the second stage, acrolein product from the first stage isconverted to acrylic acid using a catalyst composed of mainly molybdenumand vanadium oxides. In most cases, the catalyst formulations areproprietary to the catalyst supplier, but, the technology is wellestablished. Moreover, there is an incentive to develop a single stepprocess to prepare the unsaturated acid from its corresponding alkene.Therefore, the prior art describes cases where complex metal oxidecatalysts are utilized for the preparation of unsaturated acid from acorresponding alkene in a single step.

Japanese Laid-Open Patent Application Publication No. 07-053448discloses the manufacture of acrylic acid by the gas-phase catalyticoxidation of propene in the presence of mixed metal oxides containingMo, V, Te, O and X wherein X is at least one of Nb, Ta, W, Ti, Al, Zr,Cr, Mn, Fe, Ru, Co, Rh, Ni, Pd, Pt, Sb, Bi, B, In, Li, Na, K, Rb, Cs andCe.

Commercial incentives also exist for producing acrylic acid using alower cost propane feed. Therefore, the prior art describes caseswherein a mixed metal oxide catalyst is used to convert propane toacrylic acid in one step.

U.S. Pat. No. 5,380,933 discloses a method for producing an unsaturatedcarboxylic acid comprising subjecting an alkane to a vapor phasecatalytic oxidation reaction in the presence of a catalyst containing amixed metal oxide comprising, as essential components, Mo, V, Te, O andX, wherein X is at least one element selected from the group consistingof niobium, tantalum, tungsten, titanium, aluminum, zirconium, chromium,manganese, iron, ruthenium, cobalt, rhodium, nickel, palladium,platinum, antimony, bismuth, boron, indium and cerium; and wherein theproportions of the respective essential components, based on the totalamount of the essential components, exclusive of oxygen, satisfy thefollowing relationships:

0.25<r(Mo)<0.98, 0.003<r(V)<0.5, 0.003<r(Te)<0.5 and 0.003<r(X)<0.5,wherein r(Mo), r(V), r(Te) and r(X) are the molar fractions of Mo, V, Teand X, respectively, based on the total amount of the essentialcomponents exclusive of oxygen.

Nonetheless, the prior art continues to seek ways to improve theperformance of such mixed metal oxide catalysts.

For example, Ueda, et al., “Hydrothermal Synthesis of Mo—V—M—O ComplexMetal Oxide Catalysts Active For Partial Oxidation Of Ethane”, Chem.Commun., 1999, pp. 517–518, discloses Mo—V—M—O (M=Al, Fe, Cr or Ti)complex metal oxide catalysts prepared by hydrothermal synthesis, whichexhibit activity for the partial oxidation of ethane to ethene andacetic acid.

Ueda, et al., “Selective Oxidation Of Light Alkanes Over Mo-Based OxideCatalysts”, Res, Chem. Intermed., Vol. 26, No. 2, pp. 137–144 (2000)discloses that Anderson-type heteropoly compounds linked with vanadylcations, VO⁺², were synthesized by hydrothermal reaction and showed goodcatalytic activity for the oxidation of ethene to acetic acid.

Watanabe, et al., “New Synthesis Route For Mo—V—Nb—Te Mixed Metal OxidesFor Propane Ammoxidation”, Applied Catalysis A: General, 194–195, pp.479–485 (2000) discloses an examination of several methods for preparingMo—V—Nb—Te mixed oxides. Hydrothermal treatment was shown to give aprecursor of an ammoxidation catalyst which shows activity twice ashigh, after calcination, as the catalyst prepared by the known dry-upmethod. Mixed oxides prepared by a solid state reaction gave poorcatalytic activity.

Ueda, et al., “Selective Oxidation of Light Alkanes Over HydrothermallySynthesized Mo—V—M—O (M=Al, Ga, Bi, Sb and Te) Oxide Catalysts”, AppliedCatalysis A: General, 200, pp. 135–143 (2000) discloses selectiveoxidations of ethane to ethene and acetic acid, and of propane toacrylic acid, carried out over hydrothermally synthesized Mo—V—M—O(M=Al, Ga, Bi, Sb and Te) complex metal oxide catalysts. The solids wereclassified into two groups, i.e. Mo—V—M—O (M=Al, possibly Ga and Bi) andMo—V—M—O (M=Sb and Te). The former were moderately active for thepartial oxidation of ethane to ethene and acetic acid. The latter wereextremely active for the oxidative dehydrogenation and were also activefor the partial oxidation of propane to acrylic acid. Grinding of thecatalysts, after heat treatment at 600° C. in N₂, increased theconversion of propane and enhanced the selectivity to acrylic acid.

Chen, et al., “Selective Oxidation Of Ethane Over HydrothermallySynthesized Mo—V—Al—Ti Oxide Catalyst”, Catalysis Today, 64, pp. 121–128(2001) discloses synthesis of a monophasic material, Mo₆V₂Al₁O_(x), bythe hydrothermal method, which shows activity for gas-phase oxidation ofethane to ethene and acetic acid. Addition of titanium to theMo₆V₂Al₁O_(x) oxide catalyst resulted in a marked increase of theactivity for the ethane selective oxidation.

It has now been found that certain novel mixed metal oxide catalysts,which may be prepared by a hydrothermal synthesis technique, may beutilized for the partial oxidation of an alkane, or a mixture of analkane and an alkene, to produce an unsaturated carboxylic acid; or forthe ammoxidation of an alkane, or a mixture of an alkane and an alkene,to produce an unsaturated nitrile.

Thus, in a first aspect, the present invention provides a catalystcomprising a mixed metal oxide having the empirical formulaMO_(a)V_(b)M_(c)X_(d)O_(e)

-   -   wherein M is an element selected from the group consisting of        Te, Sb and Nb,    -   wherein X is an element selected from the group consisting of        Sc, Y, La, Re, Ir, Cu,    -   Ag, Au, Zn, Ga, Si, Ge, As, Pb, S, Se, Sn, Bi, F, Cl, Br and I,        and    -   wherein, when a=1, b=0.01 to 1.0, c=0.01 to 1.0, d=0 to 1 and e        is dependent on the oxidation state of the other elements;    -   with the proviso that, when d=0, M is selected from the group        consisting of Nb and Te, and    -   with the further proviso that, when d=0 and M=Te, 0.01≦b<0.50 or        0.17<c≦1.0.

In a second aspect, the present invention provides a process forproducing a catalyst comprising a mixed metal oxide having the empiricalformulaMO_(a)V_(b)M_(c)X_(d)O_(e)

-   -   wherein M is an element selected from the group consisting of        Te, Sb and Nb,    -   wherein X is an element selected from the group consiting of Sc,        Y, La, Re, Ir, Cu,    -   Ag, Au, Zn, Ga, Si, Ge, As, Pb, S, Se, Sn, Bi, F, Cl, Br and I,        and    -   wherein, when a=1, b=0.01 to 1.0, c=0.01 to 1.0, d=0 to 1 and e        is dependent on the oxidation state of the other elements;    -   with the proviso that, when d=0, M is selected from the group        consisting of Nb and Te, and    -   with the further proviso that, when d=0 and M=Te, 0.01≦b<0.50 or        0.17<c≦1.0,        the process comprising:    -   (i) admixing compounds of elements Mo, V, M and X, as needed,        and a solvent comprising water to form a first admixture        containing at least 2 but less than all of said elements Mo, V,        M and X;    -   (ii) heating said first admixture at a temperature of from        80° C. to 150° C. for from 5 minutes to 48 hours;    -   (iii) then, admixing compounds of elements Mo, V, M and X, as        needed, with said first admixture to form a second admixture        containing elements Mo, V, M and X, in the respective relative        atomic proportions a, b, c and d, wherein, when a=1, b=0.01 to        1.0, c=0.01 to 1.0 and d=0 to 1;    -   (iv) heating said second admixture at a temperature of from        50° C. to 300° C. for from 1 hour to several weeks, in a closed        vessel under pressure;    -   (v) recovering insoluble material from said closed vessel to        obtain a catalyst.

In a third aspect, the present invention provides a process forproducing an unsaturated carboxylic acid which comprise subjecting analkane, or a mixture of an alkane and an alkene, to a vapor phasecatalytic oxidation reaction in the presence of a catalyst according tothe first aspect of the invention.

In a fourth aspect, the present invention provides processes forproducing an unsaturated nitrile which comprise subjecting an alkane, ora mixture of an alkane and an alkene, and ammonia to a vapor phasecatalytic oxidation reaction in the presence of a catalyst according tothe first aspect of the invention.

The catalyst of the present invention comprises a mixed metal oxidehaving the empirical formulaMO_(a)V_(b)M_(c)X_(d)O_(e)

-   wherein M is an element selected from the group consisting of Te, Sb    and Nb,-   wherein X is an element selected from the group consisting of Sc, Y,    La, Re, Ir, Cu, Ag, Au,-   Zn, Ga, Si, Ge, As, Pb, S, Se, Sn, Bi, F, Cl, Br and I, and-   wherein, when a=1, b=0.01 to 1.0, c=0.01 to 1.0, d=0 to 1 and e is    dependent on the oxidation state of the other elements;-   with the proviso that, when d=0, M is selected fom the group    consisting of Nb and Te, and-   with the further proviso that, when d=0 and M=Te, 0.01≦b<0.50 or    0.17≦c<1.0.

Preferably, in the case where d>0, when a=1, b=0.1 to 0.6, c=0.1 to 0.5and d=0.0001 to 0.5; more preferably, b=0.3 to 0.6, c=0.15 to 0.5 andd=0.001 to 0.1. The value of e, i.e. the amount of oxygen present, isdependent on the oxidation state of the other elements in the catalyst.

A catalyst of the aforementioned composition may be prepared by anysuitable technique.

For example, the catalyst may be prepared by the “dry up” method. In the“dry up” method:

-   -   compounds of elements Mo, V, M and X and at least one solvent        are admixed to form an admixture,    -   wherein M is an element selected from the group consisting of        Te, Sb and Nb, X is an element selected from the group        consisting of Sc, Y, La, Re, Ir, Cu, Ag, Au, Zn, Ga,    -   Si, Ge, As, Pb, S, Se, Sn, Bi, F, Cl, Br and I,    -   wherein Mo, V, M and X are present in such amounts that the        atomic ratio of Mo:V:M:X is a:b:c:d, and    -   wherein, when a=1, b=0.01 to 1.0, c=0.01 to 1.0, d=0.01 to 1.0,    -   with the proviso that, when d=0, M is selected from the group        consisting of Nb and Te, and    -   with the further proviso that, when d=0 and M=Te, 0.01≦b<0.50 or        0.17≦c<1.0;    -   removing the at least one solvent from said admixture to form a        catalyst precursor; and    -   calcining the catalyst precursor to obtain said catalyst.

Suitable solvents include water; alcohols including, but not limited to,methanol, ethanol, propanol, and diols, etc.; as well as other polarsolvents known in the art. Generally, water is preferred. The water isany water suitable for use in chemical syntheses including, withoutlimitation, distilled water and de-ionized water. The amount of waterpresent is preferably an amount sufficient to keep the elementssubstantially in solution long enough to avoid or minimize compositionaland/or phase segregation during the preparation steps. Accordingly, theamount of water will vary according to the amounts and solubilities ofthe materials combined. However, as stated above, the amount of water ispreferably sufficient to ensure an aqueous solution is formed, at thetime of mixing.

The solvent is removed from the admixture by any suitable method, knownin the art, to form a catalyst precursor. Such methods include, withoutlimitation, vacuum drying, freeze drying, spray drying, rotaryevaporation and air drying.

For example, in the case of water being the solvent: Vacuum drying isgenerally performed at pressures ranging from 10 mmHg to 500 mmHg.Freeze drying typically entails freezing the solution, using, forinstance, liquid nitrogen, and drying the frozen solution under vacuum.Spray drying is generally performed under an inert atmosphere such asnitrogen or argon, with an inlet temperature ranging from 125° C. to200° C. and an outlet temperature ranging from 75° C. to 150° C. Rotaryevaporation is generally performed at a bath temperature of from 25° C.to 90° C. and at a pressure of from 10 mmHg to 760 mmHg, preferably at abath temperature of from 40° C. to 90° C. and at a pressure of from 10mmHg to 350 mmHg, more preferably at a bath temperature of from 40° C.to 60° C. and at a pressure of from 10 mmHg to 40 mmHg. Air drying maybe effected at temperatures ranging from 25° C. to 90° C. Rotaryevaporation or air drying are generally preferred.

Once obtained, the catalyst precursor is calcined. The calcination maybe conducted in an oxygen-containing atmosphere or in the substantialabsence of oxygen, e.g., in an inert atmosphere or in vacuo. The inertatmosphere may be any material which is substantially inert, i.e., doesnot react or interact with, the catalyst precursor. Suitable examplesinclude, without limitation, nitrogen, argon, xenon, helium or mixturesthereof. Preferably, the inert atmosphere is argon or nitrogen. Theinert atmosphere may flow over the surface of the catalyst precursor ormay not flow thereover (a static environment). When the inert atmospheredoes flow over the surface of the catalyst precursor, the flow rate canvary over a wide range, e.g., at a space velocity of from 1 to 500 hr⁻¹.

The calcination is usually performed at a temperature of from 350° C. to850° C., preferably from 400° C. to 700° C., more preferably from 500°C. to 650° C. The calcination is performed for an amount of timesuitable to form the aforementioned catalyst. Typically, the calcinationis performed for from 0.5 to 30 hours, preferably from 1 to 25 hours,more preferably for from 1 to 15 hours, to obtain the desired promotedmixed metal oxide.

In one mode of operation, the catalyst precursor is calcined in twostages, i.e. the catalyst precursor is heated to a first temperature inan oxidizing atmosphere and, then, the so-treated catalyst precursor isheated from the first temperature to a second temperature in anon-oxidizing atmosphere. Typically, in the first stage, the catalystprecursor is calcined in an oxidizing environment (e.g. air) at atemperature of from 200° C. to 400° C., preferably from 275° C. to 325°C. for from 15 minutes to 8 hours, preferably for from 1 to 3 hours. Inthe second stage, the material from the first stage is calcined in anon-oxidizing environment (e.g., an inert atmosphere) at a temperatureof from 500° C. to 750° C., preferably for from 550° C. to 650° C., for15 minutes to 8 hours, preferably for from 1 to 3 hours. Optionally, areducing gas, such as, for example, ammonia or hydrogen, may be addedduring the second stage calcination.

In a preferred mode of operation, the catalyst precursor in the firststage is placed in the desired oxidizing atmosphere at room temperatureand then raised to the first stage calcination temperature and heldthere for the desired first stage calcination time. The atmosphere isthen replaced with the desired non-oxidizing atmosphere for the secondstage calcination, the temperature is raised to the desired second stagecalcination temperature and held there for the desired second stagecalcination time.

Although any type of heating mechanism, e.g., a furnace, may be utilizedduring the calcination, it is preferred to conduct the calcination undera flow of the designated gaseous environment. Therefore, it isadvantageous to conduct the calcination in a bed with continuous flow ofthe desired gas(es) through the bed of solid catalyst precursorparticles.

In a particularly preferred mode of operation, the catalyst precursor inthe first stage of calcination is placed in a desired flowing oxidizingatmosphere at room temperature and then raised to the first stagecalcination temperature, at a rate of from 1° C./min to 20° C./min,preferably 2°/min to 10° C./min. It is then held at the first stagecalcination temperature, in the desired flowing oxidizing atmosphere,for the desired first stage calcination time. After the desired firststage calcination time has passed, the atmosphere is replaced with adesired flowing non-oxidizing atmosphere, preferably while maintainingthe temperature at the first stage calcination temperature; thetemperature is then raised to the desired second stage calcinationtemperature at a rate of from 1° C./min to 20° C./min, preferably 2°C./min to 10° C./min. It is then held at the second stage calcinationtemperature, in the desired flowing non-oxidizing atmosphere, for thedesired second stage calcination time.

With calcination, a catalyst is formed having the formulaMo_(a)V_(b)M_(c)X_(d)O_(e) wherein M. X, a, b, c, d and e are aspreviously defined.

Preferably, in a second aspect of the present invention, the catalyst isformed by a “hydrothermal” technique. In this “hydrothermal” technique:

compounds of elements Mo, V, M and X, as needed, and a solventcomprising water are mixed to form a first admixture containing at least2 but less than all of said elements Mo, V, M and X;

the first admixture is heated at a temperature of from 80° C. to 150° C.for from 5 minutes to 48 hours;

then, compounds of elements Mo, V, M and X, as needed, are mixed withthe first admixture to form a second admixture containing elements Mo,V, M and X, in the respective atomic proportions a, b, c and d, wherein,when a=1, b=0.01 to 1.0, c=0.01 to 1.0 and d=0 to 1;

the second admixture is heated at a temperature of from 50° C. to 300°C. for from 1 hour to several weeks, in a closed vessel under pressure;and

insoluble material is recovered from the closed vessel to obtain acatalyst.

Optionally, albeit preferably, the recovered insoluble material iscalcined.

In particular, compounds of elements Mo, V, M and X and a solventcomprising water are mixed to form a first admixture. This firstadmixture contains at least 2, but less than all, of the elements Mo, V,M and X needed to make the desired catalyst composition, wherein M is anelement selected from the group consisting of Te, Sb and Nb, X is anelement selected from the group consisting of Sc, Y, La, Re, Ir, Cu, Ag,Au, Zn, Ga, Si, Ge, As, Pb, S, Se, Sn, Bi, F, Cl, Br and I, wherein Mo,V, M and X are present in such amounts that the atomic ratio of Mo:V:M:Xis a:b:c:d, and wherein, when a=1, b=0.01 to 1.0, c=0.01 to 1.0, d=0.01to 1.0, with the proviso that, when d=0, M is selected from the groupconsisting of Nb and Te, and with the further proviso that, when d=0 andM=Te, 0.01≦b<0.50 or 0.17<c≦.1. In the case of a catalyst containing theelements Mo, V, M and X (d>0), it is preferred to mix compounds of theelements Mo, M and X, compounds of the elements Mo and M or compounds ofthe elements V and M to form the first admixture. In the case of acatalyst containing the elements Mo, V and M (d=0), it is preferred tomix compound of the elements Mo and M or compounds of the elements V andM to form the first admixture. In either case, it is preferable toutilize the components of the first admixture in the atomic proportionsof the elements present in the final catalyst.

The so-formed first admixture may be held at a temperature of 25° C. to200° C., preferably 50° C. to 175° C., most preferably 75° C. to 150°C., for from 5 minutes to 48 hours, preferably 5 minutes to 10 hours,most preferably 5 minutes to 5 hours. Any solvent or any portion of thesolvent that evaporates from the admixture during this treatment may becondensed and returned to the admixture, if so desired, in order tomaintain a liquid phase. Alternatively, this treatment of the firstadmixture may be carried out in a closed container.

Subsequent to the aforementioned treatment of the first admixture, thefirst admixture is mixed with compounds of the elements Mo, V, M and X,as needed, to form a second admixture containing elements Mo, V, M andX, in the respective atomic proportions a, b, c and d, wherein, whena=1, b=0.01 to 1.0, c=0.01 to 1.0 and d=0 to 1. Preferably, onlycompounds of elements missing from the first admixture are added in thismixing procedure.

The second admixture is then held at a temperature of 50° C. to 300° C.,preferably 100° C. to 250° C., most preferably 150° C. to 200° C., forfrom 1 hour to several weeks, preferably 2 hours to 7 days, mostpreferably 5 to 72 hours, in a closed vessel. The closed vessel may beunder pressure. The pressure may be the autogenous pressure of theenclosed materials at the particular temperature utilized or it can bean applied pressure, such as could be obtained by feeding a pressurizedgaseous atmosphere to the closed vessel. In either case, a gas spaceover the enclosed admixture may comprise an oxidizing atmosphere such asair, oxygen enriched air or oxygen; a reducing atmosphere such ashydrogen; an inert atmosphere such as nitrogen, argon, helium ormixtures thereof; or mixtures thereof. Moreover, the gas space over theenclosed admixture may be charged with low levels of catalyst promoterssuch as NO_(x) compounds, SO_(x) compounds, gaseous halides or halogens.

After the aforementioned treatment, insoluble material is recovered fromthe closed vessel. This insoluble material is a very active catalyst,but the selectivity for the desired reaction product, e.g., acrylicacid, is generally poor. When the recovered insoluble material issubjected to calcination, the activity is decreased but the selectivityfor the desired reaction product, e.g., acrylic acid, is increased.

In the “hydrothermal” technique, water is preferably used as the solventin the catalyst preparation. The water is any water suitable for use inchemical syntheses including, without limitation, distilled water andde-ionized water. However, the solvent utilized may further comprisepolar solvents such as, for example, water-miscible alcohols, diols,glycols, polyols, ethers, carboxylates, nitrites and amides. The amountof solvent utilized is not critical.

Preferably, the vessel utilized for hydrothermal treatment is formed ofa material inert to the hydrothermal reaction or is lined with amaterial inert to the hydrothermal reaction, e.g.,polytetrafluoroethylene (PTFE).

After hydrothermal treatment, insoluble material is recovered from thetreating vessel. The insoluble material may be recovered by anyconventional method, e.g., centrifugation or filtration. Preferably thehydrothermally treated material is cooled prior to recovery of theinsoluble material. If desired, the insoluble material may be washed oneor more times with water.

The recovered insoluble material may then be dried by any suitablemethod known in the art. Such methods include, without limitation,vacuum drying, freeze drying and air drying.

For example, in order to remove any residual water: Vacuum drying isgenerally performed at pressures ranging from 10 mmHg to 500 mmHg, withor without the application of heat. Freeze drying typically entailsfreezing the recovered material, using , for instance, liquid nitrogen,and drying the frozen material under vacuum. Air drying may be effectedat temperatures ranging from 25° C. to 90° C.

Calcination of the recovered insoluble material may be conducted in anoxidizing atmosphere, e.g., in air, oxygen-enriched air or oxygen, or inthe substantial absence of oxygen, e.g., in an inert atmosphere or invacuo. The inert atmosphere may be any material which is substantiallyinert, i.e., does not react or interact with, the catalyst precursor.Suitable examples include, without limitation, nitrogen, argon, xenon,helium or mixtures thereof. Preferably, the inert atmosphere is argon ornitrogen. The inert atmosphere may flow over the surface of the catalystprecursor or may not flow thereover (a static environment). When theinert atmosphere does flow over the surface of the catalyst precursor,the flow rate can vary over a wide range, e.g., at a space velocity offrom 1 to 500 hr⁻¹.

The calcination is usually performed at a temperature of from 350° C. to850° C., preferably from 400° C. to 700° C., more preferably from 500°C. to 640° C. The calcination is performed for an amount of timesuitable to form the aforementioned catalyst. Typically, the calcinationis performed for from 0.5 to 30 hours, preferably from 1 to 25 hours,more preferably for from 1 to 15 hours, to obtain the desired promotedmixed metal oxide.

In a preferred mode of operation, calcination is conducted in twostages, i.e. the recovered insoluble material is heated to a firsttemperature in an oxidizing atmosphere and, then, the so-treatedrecovered insoluble material is heated from the first temperature to asecond temperature in a non-oxidizing atmosphere. Typically, in thefirst stage, the catalyst precursor is calcined in an oxidizingenvironment (e.g. air) at a temperature of from 200° C. to 400° C.,preferably from 275° C. to 325° C. for from 15 minutes to 8 hours,preferably for from 1 to 3 hours. In the second stage, the material fromthe first stage is calcined in a non-oxidizing environment (e.g., aninert atmosphere) at a temperature of from 500° C. to 750° C.,preferably for from 550° C. to 650° C., for 15 minutes to 8 hours,preferably for from 1 to 3 hours. Optionally, a reducing gas, such as,for example, ammonia or hydrogen, may be added during the second stagecalcination.

In a particularly preferred mode of operation, in the first stage, thematerial to be calcined is placed in the desired oxidizing atmosphere atroom temperature and then raised to the first stage calcinationtemperature and held there for the desired first stage calcination time.The atmosphere is then replaced with the desired non-oxidizingatmosphere for the second stage calcination, the temperature is raisedto the desired second stage calcination temperature and held there forthe desired second stage calcination time.

In an another preferred mode of operation, the insoluble materialrecovered from the contact mixture is calcined in a non-oxidizingatmosphere, preferably an inert atmosphere. In the case where thepromoter element, i.e. the element X is a halogen, such halogen may beadded to the aforementioned non-oxidizing atmosphere.

Although any type of heating mechanism, e.g., a furnace, may be utilizedduring the calcination, it is preferred to conduct the calcination undera flow of the designated gaseous environment. Therefore, it isadvantageous to conduct the calcination in a bed with continuous flow ofthe desired gas(es) through the bed of solid catalyst precursorparticles.

The starting materials for the above mixed metal oxide are notparticularly limited. A wide range of materials including, for example,oxides, nitrates, halides or oxyhalides, alkoxides, acetylacetonates,and organometallic compounds may be used. For example, ammoniumheptamolybdate may be utilized for the source of molybdenum in thecatalyst. However, compounds such as MoO₃, MoO₂, MoCl₅, MoOCl₄,Mo(OC₂H₅)₅, molybdenum acetylacetonate, phosphomolybdic acid andsilicomolybdic acid may also be utilized instead of ammoniumheptamolybdate. Similarly, vanadyl sulfate (VOSO₄) may be utilized forthe source of vanadium in the catalyst. However, compounds such as V₂O₅,V₂O₃, VOCl₃, VCl₄, VO(OC₂H₅)₃, vanadium acetylacetonate and vanadylacetylacetonate may also be utilized instead of vanadyl sulfate. TeO₂may be utilized for the source of tellurium in the catalyst. However,TeCl₄, Te(OC₂H₅)₅ and Te(OCH(CH₃)₂)₄ may also be utilized instead ofTeO₂. The niobium source may include ammonium niobium oxalate, Nb₂O₅,NbCl₅, niobic acid or Nb(OC₂H₅)₅ as well as the more conventionalniobium oxalate.

With respect to the other elements or compounds thereof that may beutilized to make the improved catalysts of the present invention, noparticular restrictions are placed thereon. With this in mind, thefollowing lists are merely illustrative of available sources of some ofthese elements or the compounds thereof, and are not meant to belimiting hereon.

The gold source may be ammonium tetrachloroaurate, gold bromide, goldchloride, gold cyanide, gold hydroxide, gold iodide, gold oxide, goldtrichloride acid or gold sulfide.

The silver source may be silver acetate, silver acetylacetonate, silverbenzoate, silver bromide, silver carbonate, silver chloride, silvercitrate hydrate, silver fluoride, silver iodide, silver lactate, silvernitrate, solver nitrite, silver oxide, silver phosphate, or a solutionof silver in an aqueous inorganic acid, e.g., nitric acid.

The copper source may be copper acetate, copper acetate monohydrate,copper acetate hydrate, copper acetylacetonate, copper bromide, coppercarbonate, copper chloride, copper chloride dihydrate, copper fluoride,copper formate hydrate, copper gluconate, copper hydroxide, copperiodide, copper methoxide, copper nitrate hydrate, copper nitrate, copperoxide, copper tartrate hydrate, or a solution of copper in an aqueousinorganic acid, e.g., nitric acid.

The yittrium source may be an yittrium salt, e.g., yittrium nitrate,dissolved in water.

The scandium source may be scandium acetate, scandium bromide hydrate,scandium chloride, scandium chloride hexahydrate, scandium chloridehydrate, scandium fluoride, scandium iodide, scandium isopropoxide,scandium nitrate hydrate, scandium oxalate hydrate, scandium oxide, or asolution of scandium in an aqueous inorganic acid, e.g., nitric acid.

The rhenium source may be ammonium perrhenate, rhenium carbonyl, rheniumchloride, rhenium fluoride, rhenium oxide, rhenium pentacarbonylbromide, rhenium pentacarbonyl chloride and rhenium sulfide.

The iridium source may be iridium acetylacetonate, iridium bromidehydrate, iridium chloride, iridium chloride hydrochloride hydrate,iridium chloride hydrate, iridium oxide, iridium oxide hydrate, iridiumoxoacetate trihydrate or iridium dissolved in an aqueous inorganic acid,e.g., nitric acid.

The zinc source may be zinc acetate, zinc acetylacetonate, zincacrylate, zinc bis(2,2,6,6-tetramethyl-3,5-heptanedioate), zinc bromide,zinc carbonate hydroxide, zinc chloride, zinc citrate, zinccyclohexanebutyrate, zinc 3,5-di-tert-butylsalicylate, zinc fluoride,zinc iodide, zinc L-lactate, zinc methacrylate, zinc nitrate, zincoxide, zinc perchlorate or zinc stearate.

The gallium source may be Ga₂O, GaCl₃, GaCl₂, gallium acetylacetonate,Ga₂O₃ or Ga(NO₃)₃.

The bromine source may be added as one of the above reagents as abromide, e.g., as the bromide salt of X (where X is at least one elementselected from the group consisting of W, Ta, Ti, Al, Zr, Cr, Mn, Fe, Ru,Co, Rh, Ni, Pt, B, In, As, Ge, Sn, Li, Na, K, Rb, Cs, Fr, Be, Mg, Ca,Sr, Ba, Hf, Pb, P, Pm, Eu, Gd, Dy, Ho, Er, Tm, Yb and Lu), for example,as molybdenum bromide, tellurium tetrabromide or vanadium bromide; or asa solution of bromine in an aqueous inorganic acid, e.g., nitric acid.The bromine source may also be added during the calcination of therecovered insoluble material or, after calcination, as a brominetreatment step. For example, the bromine source may be added to thecalcination atmosphere or to the oxidation or ammoxidation reactor feedstream, as, for example, HBr, Br₂, ethyl bromide or the like, to achievea promotional effect with the bromine.

The chlorine source may also be added as one of the above reagents as achloride, e.g., as the chloride salt of X (where X is at least oneelement selected from the group consisting of W, Ta, Ti, Al, Zr, Cr, Mn,Fe, Ru, Co, Rh, Ni, Pt, B, In, As, Ge, Sn, Li, Na, K, Rb, Cs, Fr, Be,Mg, Ca, Sr, Ba, Ra, Hf, Pb, P, Pm, Eu, Gd, Dy, Ho, Er, Tm, Yb and Lu),for example, as molybdenum chloride, tellurium tetrachloride or vanadiumchloride. The chlorine source may also be added during the calcinationof the recovered insoluble material or, after calcination, as a chlorinetreatment step. For example, the chlorine source may be added to thecalcination atmosphere or to the oxidation or ammoxidation reactor feedstream, as, for example, HCl, Cl₂, ethyl chloride or the like, toachieve a promotional effect with the chloride.

The fluorine source may be added as one of the above reagents as afluoride, e.g., as the fluoride salt of X (where X is at least oneelement selected from the group consisting of W, Ta, Ti, Al, Zr, Cr, Mn,Fe, Ru, Co, Rh, Ni, Pt, B, In, As, Ge, Sn, Li, Na, K, Rb, Cs, Fr, Be,Mg, Ca, Sr, Ba, Ra, Hf, Pb, P, Pm, Eu, Gd, Dy, Ho, Er, Tm, Yb and Lu),for example, as molybdenum fluoride, tellurium fluoride or vanadiumfluoride. The fluorine source may also be added during the calcinationof the recovered insoluble material or, after calcination, as a fluorinetreatment step. For example, the fluorine source may be added to thecalcination atmosphere or to the oxidation or ammoxidation reactor feedstream, as, for example, HF, F₂, ethyl fluoride or the like, to achievea promotional effect with the fluoride.

The iodine source may be added as one of the above reagents as afluoride, e.g., as the fluoride salt of X (where X is at least oneelement selected from the group consisting of W, Ta, Ti, Al, Zr, Cr, Mn,Fe, Ru, Co, Rh, Ni, Pt, B, In, As, Ge, Sn, Li, Na, K, Rb, Cs, Fr, Be,Mg, Ca, Sr, Ba, Ra, Hf, Pb, P, Pm, Eu, Gd, Dy, Ho, Er, Tm, Yb and Lu),for example, as molybdenum iodide, tellurium iodide or vanadium iodide.The iodine source may also be added during the calcination of therecovered insoluble material or, after calcination, as an iodinetreatment step. For example, the iodine source may be added to thecalcination atmosphere or to the oxidation or ammoxidation reactor feedstream, as, for example, HI, I₂, ethyl iodide or the like, to achieve apromotional effect with the iodide.

The catalyst formed by the aforementioned techniques, exhibits goodcatalytic activities by itself. However, the mixed metal oxide may beconverted to a catalyst having higher activities by grinding.

There is no particular restriction as to the grinding method, andconventional methods may be employed. As a dry grinding method, a methodof using a gas stream grinder may, for example, be mentioned whereincoarse particles are permitted to collide with one another in a highspeed gas stream for grinding. The grinding may be conducted not onlymechanically but also by using a mortar or the like in the case of asmall scale operation.

As a wet grinding method wherein grinding is conducted in a wet state byadding water or an organic solvent to the above mixed metal oxide, aconventional method of using a rotary cylinder-type medium mill or amedium-stirring type mill, may be mentioned. The rotary cylinder-typemedium mill is a wet mill of the type wherein a container for the objectto be ground is rotated, and it includes, for example, a ball mill and arod mill. The medium-stirring type mill is a wet mill of the typewherein the object to be ground, contained in a container is stirred bya stirring apparatus, and it includes, for example, a rotary screw typemill, and a rotary disc type mill.

The conditions for grinding may suitably be set to meet the nature ofthe above-mentioned promoted mixed metal oxide, the viscosity, theconcentration, etc. of the solvent used in the case of wet grinding, orthe optimum conditions of the grinding apparatus.

Further, in some cases, it is possible to further improve the catalyticactivities by further adding a solvent to the ground catalyst precursorto form a solution or slurry, followed by drying again. There is noparticular restriction as to the concentration of the solution orslurry, and it is usual to adjust the solution or slurry so that thetotal amount of the starting material compounds for the ground catalystprecursor is from 10 to 60 wt %. Then, this solution or slurry is driedby a method such as spray drying, freeze drying, evaporation to drynessor vacuum drying, preferably by the spray drying method. Further,similar drying may be conducted also in the case where wet grinding isconducted.

The oxide obtained by the above-mentioned method may be used as a finalcatalyst, but it may further be subjected to heat treatment usually at atemperature of from 200° to 700° C. for from 0.1 to 10 hours.

The mixed metal oxide thus obtained may be used by itself as a solidcatalyst, but may be formed into a catalyst together with a suitablecarrier such as silica, alumina, titania, aluminosilicate, diatomaceousearth or zirconia. Further, it may be molded into a suitable shape andparticle size depending upon the scale or system of the reactor.

In its third aspect, the present invention provides a process forproducing an unsaturated carboxylic acid, which comprises subjecting analkane, or a mixture of an alkane and an alkene, to a vapor phasecatalytic oxidation reaction in the presence of a catalyst according tothe first aspect of the invention.

In the production of such an unsaturated carboxylic acid, it ispreferred to employ a starting material gas which contains steam. Insuch a case, as a starting material gas to be supplied to the reactionsystem, a gas mixture comprising a steam-containing alkane, or asteam-containing mixture of alkane and alkene, and an oxygen-containinggas, is usually used. However, the steam-containing alkane, or thesteam-containing mixture of alkane and alkene, and the oxygen-containinggas may be alternately supplied to the reaction system. The steam to beemployed may be present in the form of steam gas in the reaction system,and the manner of its introduction is not particularly limited.

In regard to the use of a halogen as an element of the catalyst of thepresent invention, it is possible to add a gaseous halogen source aspreviously identified to the gas feed to the reaction.

Further, as a diluting gas, an inert gas such as nitrogen, argon orhelium may be supplied. The molar ratio (alkane or mixture of alkane andalkene):(oxygen):(diluting gas):(H₂O) in the starting material gas ispreferably (1):(0.1 to 10):(0 to 20):(0.2 to 70), more preferably (1):(1to 5.0):(0 to 10):(5 to 40).

When steam is supplied together with the alkane, or the mixture ofalkane and alkene, as starting material gas, the selectivity for anunsaturated carboxylic acid is distinctly improved, and the unsaturatedcarboxylic acid can be obtained from the alkane, or mixture of alkaneand alkene, in good yield simply by contacting in one stage. However,the conventional technique utilizes a diluting gas such as nitrogen,argon or helium for the purpose of diluting the starting material. Assuch a diluting gas, to adjust the space velocity, the oxygen partialpressure and the steam partial pressure, an inert gas such as nitrogen,argon or helium may be used together with the steam.

As the starting material alkane it is preferred to employ a C₃₋₈alkane,particularly propane, isobutane or n-butane; more preferably, propane orisobutane; most preferably, propane. According to the present invention,from such an alkane, an unsaturated carboxylic acid such as anα,β-unsaturated carboxylic acid can be obtained in good yield. Forexample, when propane or isobutane is used as the starting materialalkane, acrylic acid or methacrylic acid will be obtained, respectively,in good yield.

In the present invention, as the starting material mixture of alkane andalkene, it is possible to employ a mixture of C₃₋₈alkane and C₃₋₈alkene,particularly propane and propene, isobutane and isobutene or n-butaneand n-butene. As the starting material mixture of alkane and alkene,propane and propene or isobutane and isobutene are more preferred. Mostpreferred is a mixture of propane and propene. According to the presentinvention, from such a mixture of an alkane and an alkene, anunsaturated carboxylic acid such as an α,β-unsaturated carboxylic acidcan be obtained in good yield. For example, when propane and propene orisobutane and isobutene are used as the starting material mixture ofalkane and alkene, acrylic acid or methacrylic acid will be obtained,respectively, in good yield. Preferably, in the mixture of alkane andalkene, the alkene is present in an amount of at least 0.5% by weight,more preferably at least 1.0% by weight to 95% by weight; mostpreferably, 3% by weight to 90% by weight.

As an alternative, an alkanol, such as isobutanol, which will dehydrateunder the reaction conditions to form its corresponding alkene, i.e.isobutene, may also be used as a feed to the present process or inconjunction with the previously mentioned feed streams.

The purity of the starting material alkane is not particularly limited,and an alkane containing a lower alkane such as methane or ethane, airor carbon dioxide, as impurities, may be used without any particularproblem. Further, the starting material alkane may be a mixture ofvarious alkanes. Similarly, the purity of the starting material mixtureof alkane and alkene is not particularly limited, and a mixture ofalkane and alkene containing a lower alkene such as ethene, a loweralkane such as methane or ethane, air or carbon dioxide, as impurities,may be used without any particular problem. Further, the startingmaterial mixture of alkane and alkene may be a mixture of variousalkanes and alkenes.

There is no limitation on the source of the alkene. It may be purchased,per se, or in admixture with an alkane and/or other impurities.Alternatively, it can be obtained as a by-product of alkane oxidation.Similarly, there is no limitation on the source of the alkane. It may bepurchased, per se, or in admixture with an alkene and/or otherimpurities. Moreover, the alkane, regardless of source, and the alkene,regardless of source, may be blended as desired.

The detailed mechanism of the oxidation reaction of the presentinvention is not clearly understood, but the oxidation reaction iscarried out by oxygen atoms present in the above promoted mixed metaloxide or by molecular oxygen present in the feed gas. To incorporatemolecular oxygen into the feed gas, such molecular oxygen may be pureoxygen gas. However, it is usually more economical to use anoxygen-containing gas such as air, since purity is not particularlyrequired.

It is also possible to use only an alkane, or a mixture of alkane andalkene, substantially in the absence of molecular oxygen for the vaporphase catalytic reaction. In such a case, it is preferred to adopt amethod wherein a part of the catalyst is appropriately withdrawn fromthe reaction zone from time to time, then sent to an oxidationregenerator, regenerated and then returned to the reaction zone forreuse. As the regeneration method of the catalyst, a method may, forexample, be mentioned which comprises contacting an oxidative gas suchas oxygen, air or nitrogen monoxide with the catalyst in the regeneratorusually at a temperature of from 300° to 600° C.

This aspect of the present invention will be described in further detailwith respect to a case where propane is used as the starting materialalkane and air is used as the oxygen source. The reaction system may bea fixed bed system or a fluidized bed system. However, since thereaction is an exothermic reaction, a fluidized bed system maypreferably be employed whereby it is easy to control the reactiontemperature. The proportion of air to be supplied to the reaction systemis important for the selectivity for the resulting acrylic acid, and itis usually at most 25 moles, preferably from 0.2 to 18 moles per mole ofpropane, whereby high selectivity for acrylic acid can be obtained. Thisreaction can be conducted usually under atmospheric pressure, but may beconducted under a slightly elevated pressure or slightly reducedpressure. With respect to other alkanes such as isobutane, or tomixtures of alkanes and alkenes such as propane and propene, thecomposition of the feed gas may be selected in accordance with theconditions for propane.

Typical reaction conditions for the oxidation of propane or isobutane toacrylic acid or methacrylic acid may be utilized in the practice of thepresent invention. The process may be practiced in a single pass mode(only fresh feed is fed to the reactor) or in a recycle mode (at least aportion of the reactor effluent is returned to the reactor). Generalconditions for the process of the present invention are as follows: thereaction temperature can vary from 200° C. to 700° C., but is usually inthe range of from 200° C. to 550° C., more preferably 250° C. to 480°C., most preferably 300° C. to 400° C.; the gas space velocity, SV, inthe vapor phase reaction is usually within a range of from 100 to 10,000hr⁻¹, preferably 300 to 6,000 hr⁻¹, more preferably 300 to 2,000 hr⁻¹;the average contact time with the catalyst can be from 0.01 to 10seconds or more, but is usually in the range of from 0.1 to 10 seconds,preferably from 2 to 6 seconds; the pressure in the reaction zoneusually ranges from 0 to 75 psig, but is preferably no more than 50psig. In a single pass mode process, it is preferred that the oxygen besupplied from an oxygen-containing gas such as air. The single pass modeprocess may also be practiced with oxygen addition. In the practice ofthe recycle mode process, oxygen gas by itself is the preferred sourceso as to avoid the build up of inert gases in the reaction zone.

Of course, in the oxidation reaction of the present invention, it isimportant that the hydrocarbon and oxygen concentrations in the feedgases be maintained at the appropriate levels to minimize or avoidentering a flammable regime within the reaction zone or especially atthe outlet of the reactor zone. Generally, it is preferred that theoutlet oxygen levels be low to both minimize after-burning and,particularly, in the recycle mode of operation, to minimize the amountof oxygen in the recycled gaseous effluent stream. In addition,operation of the reaction at a low temperature (below 450° C.) isextremely attractive because after-burning becomes less of a problemwhich enables the attainment of higher selectivity to the desiredproducts. The catalyst of the present invention operates moreefficiently at the lower temperature range set forth above,significantly reducing the formation of acetic acid and carbon oxides,and increasing selectivity to acrylic acid. As a diluting gas to adjustthe space velocity and the oxygen partial pressure, an inert gas such asnitrogen, argon or helium may be employed.

When the oxidation reaction of propane, and especially the oxidationreaction of propane and propene, is conducted by the method of thepresent invention, carbon monoxide, carbon dioxide, acetic acid, etc.may be produced as by-products, in addition to acrylic acid. Further, inthe method of the present invention, an unsaturated aldehyde maysometimes be formed depending upon the reaction conditions. For example,when propane is present in the starting material mixture, acrolein maybe formed; and when isobutane is present in the starting materialmixture, methacrolein may be formed. In such a case, such an unsaturatedaldehyde can be converted to the desired unsaturated carboxylic acid bysubjecting it again to the vapor phase catalytic oxidation with thepromoted mixed metal oxide-containing catalyst of the present inventionor by subjecting it to a vapor phase catalytic oxidation reaction with aconventional oxidation reaction catalyst for an unsaturated aldehyde.

In its fourth aspect, the present invention provides a process forproducing an unsaturated nitrile, which comprises subjecting an alkane,or a mixture of an alkane and an alkene, to a vapor phase catalyticoxidation reaction with ammonia in the presence of a catalyst accordingto the first aspect of the invention.

In regard to the use of a halogen as an element of the catalyst of thepresent invention, it is possible to add a gaseous halogen source aspreviously identified to the gas feed to the reaction.

In the production of such an unsaturated nitrile, as the startingmaterial alkane, it is preferred to employ a C₃₋₈alkane such as propane,butane, isobutane, pentane, hexane and heptane. However, in view of theindustrial application of nitrites to be produced, it is preferred toemploy a lower alkane having 3 or 4 carbon atoms, particularly propaneand isobutane.

Similarly, as the starting material mixture of alkane and alkene, it ispossible to employ a mixture of C₃₋₈alkane and C₃₋₈alkene such aspropane and propene, butane and butene, isobutane and isobutene, pentaneand pentene, hexane and hexene, and heptane and heptene. However, inview of the industrial application of nitrites to be produced, it ismore preferred to employ a mixture of a lower alkane having 3 or 4carbon atoms and a lower alkene having 3 or 4 carbon atoms, particularlypropane and propene or isobutane and isobutene. Preferably, in themixture of alkane and alkene, the alkene is present in an amount of atleast 0.5% by weight, more preferably at least 1.0% by weight to 95% byweight, most preferably 3% by weight to 90% by weight.

The purity of the starting material alkane is not particularly limited,and an alkane containing a lower alkane such as methane or ethane, airor carbon dioxide, as impurities, may be used without any particularproblem. Further, the starting material alkane may be a mixture ofvarious alkanes. Similarly, the purity of the starting material mixtureof alkane and alkene is not particularly limited, and a mixture ofalkane and alkene containing a lower alkene such as ethene, a loweralkane such as methane or ethane, air or carbon dioxide, as impurities,may be used without any particular problem. Further, the startingmaterial mixture of alkane and alkene may be a mixture of variousalkanes and alkenes.

There is no limitation on the source of the alkene. It may be purchased,per se, or in admixture with an alkane and/or other impurities.Alternatively, it can be obtained as a by-product of alkane oxidation.Similarly, there is no limitation on the source of the alkane. It may bepurchased, per se, or in admixture with an alkene and/or otherimpurities. Moreover, the alkane, regardless of source, and the alkene,regardless of source, may be blended as desired.

The detailed mechanism of the ammoxidation reaction of this aspect ofthe present invention is not clearly understood. However, the oxidationreaction is conducted by the oxygen atoms present in the above promotedmixed metal oxide or by the molecular oxygen in the feed gas. Whenmolecular oxygen is incorporated in the feed gas, the oxygen may be pureoxygen gas. However, since high purity is not required, it is usuallyeconomical to use an oxygen-containing gas such as air.

As the feed gas, it is possible to use a gas mixture comprising analkane, or a mixture of an alkane and an alkene, ammonia and anoxygen-containing gas, However, a gas mixture comprising an alkane or amixture of an alkane and an alkene and ammonia, and an oxygen-containinggas may be supplied alternately.

When the gas phase catalytic reaction is conducted using an alkane, or amixture of an alkane and an alkene, and ammonia substantially free frommolecular oxygen, as the feed gas, it is advisable to employ a methodwherein a part of the catalyst is periodically withdrawn and sent to anoxidation regenerator for regeneration, and the regenerated catalyst isreturned to the reaction zone. As a method for regenerating thecatalyst, a method may be mentioned wherein an oxidizing gas such asoxygen, air or nitrogen monoxide is permitted to flow through thecatalyst in the regenerator usually at a temperature of from 300° C. to600° C.

This aspect of the present invention will be described in further detailwith respect to a case where propane is used as the starting materialalkane and air is used as the oxygen source. The proportion of air to besupplied for the reaction is important with respect to the selectivityfor the resulting acrylonitrile. Namely, high selectivity foracrylonitrile is obtained when air is supplied within a range of at most25 moles, particularly 1 to 15 moles, per mole of the propane. Theproportion of ammonia to be supplied for the reaction is preferablywithin a range of from 0.2 to 5 moles, particularly from 0.5 to 3 moles,per mole of propane. This reaction may usually be conducted underatmospheric pressure, but may be conducted under a slightly increasedpressure or a slightly reduced pressure. With respect to other alkanessuch as isobutane, or to mixtures of alkanes and alkenes such as propaneand propene, the composition of the feed gas may be selected inaccordance with the conditions for propane.

The process of this aspect of the present invention may be conducted ata temperature of, for example, from 250° C. to 480° C. More preferably,the temperature is from 300° C. to 400° C. The gas space velocity, SV,in the gas phase reaction is usually within the range of from 100 to10,000 hr⁻¹, preferably from 300 to 6,000 hr⁻¹, more preferably from 300to 2,000 hr⁻¹. As a diluent gas, for adjusting the space velocity andthe oxygen partial pressure, an inert gas such as nitrogen, argon orhelium can be employed. When ammoxidation of propane is conducted by themethod of the present invention, in addition to acrylonitrile, carbonmonoxide, carbon dioxide, acetonitrile, hydrocyanic acid and acroleinmay form as by-products.

EXAMPLES

Catalyst Preparation

Comparative Example 1

To a 45 mL Parr Acid Digestion Bomb with an inner tube made of PTFE,0.53 g of tellurium dioxide (Aldrich) and 20 mL of aqueous solution ofammonium heptamolybdate tetrahydrate (Aldrich, 1.0 M in Mo) were added,and then 10 mL of aqueous solution of vanadyl sulfate hydrate (Aldrich,1.0 M in V) was added dropwise at ambient temperature with stirring. Themixed suspension was hydrothermally treated at 175° C. for 20 hours.Black solids formed on the wall and bottom of the bomb were collected bygravity filtration, washed with deionized water (50 mL), dried in avacuum oven at 25° C. overnight, and then calcined in air from 25 to275° C. at 10° C./min and held at 275° C. for 1 hour, then in Ar from275 to 600° C. at 2° C./min and held at 600° C. for 2 hours. The finalcatalyst had a nominal composition of MoV_(0.5)Te₀₁₇Ox. The catalystthus obtained was pressed in a mold and then broken and sieved to 10–20mesh granules for reactor evaluation.

Example 1

To a 45 mL Parr Acid Digestion Bomb with an inner tube made of PTFE,0.53 g of tellurium dioxide (Aldrich), 5 mL of gallium(III) nitratehydrate in water (Aldrich, 0.1 M) and 20 mL of ammonium heptamolybdatetetrahydrate in water (Aldrich, 1.0 M in Mo) were added, and then 10 mLof vanadyl sulfate hydrate in water (Aldrich, 1.0 M in V) was addeddropwise at ambient temperature with stirring. The mixed suspension washydrothermally treated at 175° C. for 20 hours. Black solids formed onthe wall and bottom of the bomb were collected by gravity filtration,washed with deionized water (50 mL), dried in a vacuum oven at 25° C.overnight, and then calcined in air from 25 to 275° C. at 10° C./min andheld at 275° C. for 1 hour, then in Ar from 275 to 600° C. at 2° C./minand held at 600° C. for 2 hours. The final catalyst had a nominalcomposition of Ga_(0.025)MoV_(0.5)Te_(0.17)O_(x). The catalyst thusobtained was pressed in a mold and then broken and sieved to 10–20 meshgranules for reactor evaluation.

Example 2

To a 45 mL Parr Acid Digestion Bomb with an inner tube made of PTFE,0.53 g of tellurium dioxide (Aldrich), 1 mL of VBr₃ in water (Aldrich,0.1 M in Br) and 20 mL of ammonium heptamolybdate tetrahydrate in water(Aldrich, 1.0 M in Mo) were added, and then 10 mL of vanadyl sulfatehydrate in water (Aldrich, 1.0 M in V) was added dropwise at ambienttemperature with stirring. The mixed suspension was hydrothermallytreated at 175° C. for 20 hours. Black solids formed on the wall andbottom of the bomb were collected by gravity filtration, washed withdeionized water (50 mL), dried in a vacuum oven at 25° C. overnight, andthen calcined in air from 25 to 275° C. at 10° C./min and held at 275°C. for 1 hour, then in Ar from 275 to 600° C. at 2° C./min and held at600° C. for 2 hours. The final catalyst had a nominal composition ofBr_(0.005)MoV_(0.5)Te_(0.17)O_(x). The catalyst thus obtained waspressed in a mold and then broken and sieved to 10–20 mesh granules forreactor evaluation.

Example 3

To a 45 mL Parr Acid Digestion Bomb with an inner tube made of PTFE,0.53 g of tellurium dioxide (Aldrich), 1 mL of VF₃ in water (Aldrich,0.1 M in F) and 20 mL of ammonium heptamolybdate tetrahydrate in water(Aldrich, 1.0 M in Mo) were added, and then 10 mL of vanadyl sulfatehydrate in water (Aldrich, 1.0 M in V) was added dropwise at ambienttemperature with stirring. The mixed suspension was hydrothermallytreated at 175° C. for 20 hours. Black solids formed on the wall andbottom of the bomb were collected by gravity filtration, washed withdeionized water (50 mL), dried in a vacuum oven at 25° C. overnight, andthen calcined in air from 25 to 275° C. at 10° C./min and held at 275°C. for 1 hour, then in Ar from 275 to 600° C. at 2° C./min and held at600° C. for 2 hours. The final catalyst had a nominal composition ofF_(0.005)MoV_(0.5)Te_(0.17)O_(x). The catalyst thus obtained was pressedin a mold and then broken and sieved to 10–20 mesh granules for reactorevaluation.

Example 4

To a 45 mL Parr Acid Digestion Bomb with an inner tube made of PTFE,0.53 g of tellurium dioxide (Aldrich), 1 mL of Bi(NO₃)₃.5H₂O in 5%nitric acid (Aldrich, 0.1 M) and 20 mL of ammonium heptamolybdatetetrahydrate in water (Aldrich, 1.0 M in Mo) were added, and then 10 mLof vanadyl sulfate hydrate in water (Aldrich, 1.0 M in V) was addeddropwise at ambient temperature with stirring. The mixed suspension washydrothermally treated at 175° C. for 20 hours. Black solids formed onthe wall and bottom of the bomb were collected by gravity filtration,washed with deionized water (50 mL), dried in a vacuum oven at 25° C.overnight, and then calcined in air from 25 to 275° C. at 10° C./min andheld at 275° C. for 1 hour, then in Ar from 275 to 600° C. at 2° C./minand held at 600° C. for 2 hours. The final catalyst had a nominalcomposition of Bi_(0.005)MoV_(0.5)Te_(0.17)O_(x). The catalyst thusobtained was pressed in a mold and then broken and sieved to 10–20 meshgranules for reactor evaluation.

Example 5

To a 45 mL Parr Acid Digestion Bomb with an inner tube made of PTFE,0.53 g of tellurium dioxide (Aldrich), 1 mL of VI₃ in water (Aldrich,0.1 M in I) and 20 mL of ammonium heptamolybdate tetrahydrate in water(Aldrich, 1.0 M in Mo) were added, and then 10 mL of vanadyl sulfatehydrate in water (Aldrich, 1.0 M in V) was added dropwise at ambienttemperature with stirring. The mixed suspension was hydrothermallytreated at 175° C. for 20 hours. Black solids formed on the wall andbottom of the bomb were collected by gravity filtration, washed withdeionized water (50 mL), dried in a vacuum oven at 25° C. overnight, andthen calcined in air from 25 to 275° C. at 10° C./min and held at 275°C. for 1 hour, then in Ar from 275 to 600° C. at 2° C./min and held at600° C. for 2 hours. The final catalyst had a nominal composition ofI_(0.005)MoV_(0.5)Te_(0.17)O_(x). The catalyst thus obtained was pressedin a mold and then broken and sieved to 10–20 mesh granules for reactorevaluation.

Example 6

To a 45 mL Parr Acid Digestion Bomb with an inner tube made of PTFE,0.53 g of tellurium dioxide (Aldrich), 0.01 g of GeO₂ (Aldrich) and 20mL of ammonium heptamolybdate tetrahydrate in water (Aldrich, 1.0 M inMo) were added, and then 10 mL of vanadyl sulfate hydrate in water(Aldrich, 1.0 M in V) was added dropwise at ambient temperature withstirring. The mixed suspension was hydrothermally treated at 175° C. for20 hours. Black solids formed on the wall and bottom of the bomb werecollected by gravity filtration, washed with deionized water (50 mL),dried in a vacuum oven at 25° C. overnight, and then calcined in airfrom 25 to 275° C. at 10° C./min and held at 275° C. for 1 hour, then inAr from 275 to 600° C. at 2° C./min and held at 600° C. for 2 hours. Thefinal catalyst had a nominal composition ofGe_(0.005)MoV_(0.5)Te_(0.17)O_(x). The catalyst thus obtained waspressed in a mold and then broken and sieved to 10–20 mesh granules forreactor evaluation.

Example 7

To a 45 mL Parr Acid Digestion Bomb with an inner tube made of PTFE,0.53 g of tellurium dioxide (Aldrich), 5 mL of La(NO₃)₃.6H₂O in water(Aldrich, 0.1 M) and 20 mL of ammonium heptamolybdate tetrahydrate inwater (Aldrich, 1.0 M in Mo) were added, and then 10 mL of vanadylsulfate hydrate in water (Aldrich, 1.0 M in V) was added dropwise atambient temperature with stirring. The mixed suspension washydrothermally treated at 175° C. for 20 hours. Black solids formed onthe wall and bottom of the bomb were collected by gravity filtration,washed with deionized water (50 mL), dried in a vacuum oven at 25° C.overnight, and then calcined in air from 25 to 275° C. at 10° C./min andheld at 275° C. for 1 hour, then in Ar from 275 to 600° C. at 2° C./minand held at 600° C. for 2 hours. The final catalyst had a nominalcomposition of La_(0.025)MoV_(0.5)Te_(0.17)O_(x). The catalyst thusobtained was pressed in a mold and then broken and sieved to 10–20 meshgranules for reactor evaluation.

Example 8

To a 45 mL Parr Acid Digestion Bomb with an inner tube made of PTFE,0.53 g of tellurium dioxide (Aldrich), 1 mL of Y(NO₃)₃.6H₂O in water(Aldrich, 0.1 M) and 20 mL of ammonium heptamolybdate tetrahydrate inwater (Aldrich, 1.0 M in Mo) were added, and then 10 mL of vanadylsulfate hydrate in water (Aldrich, 1.0 M in V) was added dropwise atambient temperature with stirring. The mixed suspension washydrothermally treated at 175° C. for 20 hours. Black solids formed onthe wall and bottom of the bomb were collected by gravity filtration,washed with deionized water (50 mL), dried in a vacuum oven at 25° C.overnight, and then calcined in air from 25 to 275° C. at 10° C./min andheld at 275° C. for 1 hour, then in Ar from 275 to 600° C. at 2° C./minand held at 600° C. for 2 hours. The final catalyst had a nominalcomposition of Y_(0.005)MoV_(0.5)Te_(0.17)O_(x). The catalyst thusobtained was pressed in a mold and then broken and sieved to 10–20 meshgranules for reactor evaluation.

Example 9

To a 45 mL Parr Acid Digestion Bomb with an inner tube made of PTFE,1.06 g of tellurium dioxide (Aldrich), 1 mL of Y(NO₃)₃.6H₂O in water(Aldrich, 0.1 M) and 20 mL of ammonium heptamolybdate tetrahydrate inwater (Aldrich, 1.0 M in Mo) were added, and then 10 mL of vanadylsulfate hydrate in water (Aldrich, 1.0 M in V) was added dropwise atambient temperature with stirring. The mixed suspension washydrothermally treated at 175° C. for 20 hours. Black solids formed onthe wall and bottom of the bomb were collected by gravity filtration,washed with deionized water (50 mL), dried in a vacuum oven at 25° C.overnight, and then calcined in air from 25 to 275° C. at 10° C./min andheld at 275° C. for 1 hour, then in Ar from 275 to 600° C. at 2° C./minand held at 600° C. for 2 hours. The final catalyst had a nominalcomposition of Y_(0.005)MoV_(0.5)Te_(0.33)O_(x). The catalyst thusobtained was pressed in a mold and then broken and sieved to 10–20 meshgranules for reactor evaluation.

Example 10

To a 45 mL Parr Acid Digestion Bomb with an inner tube made of PTFE,0.53 g of tellurium dioxide (Aldrich), 5 mL of AgNO₃ in water (Aldrich,0.1 M) and 20 mL of ammonium heptamolybdate tetrahydrate in water(Aldrich, 1.0 M in Mo) were added, and then 10 mL of vanadyl sulfatehydrate in water (Aldrich, 1.0 M in V) was added dropwise at ambienttemperature with stirring. The mixed suspension was hydrothermallytreated at 175° C. for 20 hours. Black solids formed on the wall andbottom of the bomb were collected by gravity filtration, washed withdeionized water (50 mL), dried in a vacuum oven at 25° C. overnight, andthen calcined in air from 25 to 275° C. at 10° C./min and held at 275°C. for 1 hour, then in Ar from 275 to 600° C. at 2° C./min and held at600° C. for 2 hours. The final catalyst had a nominal composition ofAg_(0.025)MoV_(0.5)Te_(0.17)O_(x). The catalyst thus obtained waspressed in a mold and then broken and sieved to 10–20 mesh granules forreactor evaluation.

Example 11

To a 45 mL Parr Acid Digestion Bomb with an inner tube made of PTFE,0.53 g of tellurium dioxide (Aldrich), 1 mL of Zn(NO₃)₂.6H₂O in water(Aldrich, 0.1 M) and 20 mL of ammonium heptamolybdate tetrahydrate inwater (Aldrich, 1.0 M in Mo) were added, and then 10 mL of vanadylsulfate hydrate in water (Aldrich, 1.0 M in V) was added dropwise atambient temperature with stirring. The mixed suspension washydrothermally treated at 175° C. for 20 hours. Black solids formed onthe wall and bottom of the bomb were collected by gravity filtration,washed with deionized water (50 ML), dried in a vacuum oven at 25° C.overnight, and then calcined in air from 25 to 275° C. at 10° C./min andheld at 275° C. for 1 hour, then in Ar from 275 to 600° C. at 2° C./minand held at 600° C. for 2 hours. The final catalyst had a nominalcomposition of Zn_(0.005)MoV_(0.5)Te_(0.17)O_(x). The catalyst thusobtained was pressed in a mold and then broken and sieved to 10–20 meshgranules for reactor evaluation.

Example 12

To a 45 mL Parr Acid Digestion Bomb with an inner tube made of PTFE,0.53 g of tellurium dioxide (Aldrich), 0.2 mL of Au(OH)₃ in water(Aldrich, 0.1 M) and 20 mL of ammonium heptamolybdate tetrahydrate inwater (Aldrich, 1.0 M in Mo) were added, and then 10 mL of vanadylsulfate hydrate in water (Aldrich, 1.0 M in V) was added dropwise atambient temperature with stirring. The mixed suspension washydrothermally treated at 175° C. for 20 hours. Black solids formed onthe wall and bottom of the bomb were collected by gravity filtration,washed with deionized water (50 mL), dried in a vacuum oven at 25° C.overnight, and then calcined in air from 25 to 275° C. at 10° C./min andheld at 275° C. for 1 hour, then in Ar from 275 to 600° C. at 2° C./minand held at 600° C. for 2 hours. The final catalyst had a nominalcomposition of Au_(0.001)MoV_(0.5)Te_(0.17)O_(x). The catalyst thusobtained was pressed in a mold and then broken and sieved to 10–20 meshgranules for reactor evaluation.

Example 13

To a 45 mL Parr Acid Digestion Bomb with an inner tube made of PTFE,0.53 g of tellurium dioxide (Aldrich), 1 mL of H₅As₃O₁₀ in water(Aldrich, 0.1 M in As) and 20 mL of ammonium heptamolybdate tetrahydratein water (Aldrich, 1.0 M in Mo) were added, and then 10 mL of vanadylsulfate hydrate in water (Aldrich, 1.0 M in V) was added dropwise atambient temperature with stirring. The mixed suspension washydrothermally treated at 175° C. for 20 hours. Black solids formed onthe wall and bottom of the bomb were collected by gravity filtration,washed with deionized water (50 mL), dried in a vacuum oven at 25° C.overnight, and then calcined in air from 25 to 275° C. at 10° C./min andheld at 275° C. for 1 hour, then in Ar from 275 to 600° C. at 2° C./minand held at 600° C. for 2 hours. The final catalyst had a nominalcomposition of As_(0.005)MoV_(0.5)Te_(0.17)O_(x). The catalyst thusobtained was pressed in a mold and then broken and sieved to 10–20 meshgranules for reactor evaluation.

Example 14

To a 45 mL Parr Acid Digestion Bomb with an inner tube made of PTFE,0.53 g of tellurium dioxide (Aldrich), 1 mL of Pb(NO₃)₂ in water(Aldrich, 0.1 M) and 20 mL of ammonium heptamolybdate tetrahydrate inwater (Aldrich, 1.0 M in Mo) were added, and then 10 mL of vanadylsulfate hydrate in water (Aldrich, 1.0 M in V) was added dropwise atambient temperature with stirring. The mixed suspension washydrothermally treated at 175° C. for 20 hours. Black solids formed onthe wall and bottom of the bomb were collected by gravity filtration,washed with deionized water (50 mL), dried in a vacuum oven at 25° C.overnight, and then calcined in air from 25 to 275° C. at 10° C./min andheld at 275° C. for 1 hour, then in Ar from 275 to 600° C. at 2° C./minand held at 600° C. for 2 hours. The final catalyst had a nominalcomposition of Pb_(0.005)MoV_(0.5)Te_(0.17)O_(x). The catalyst thusobtained was pressed in a mold and then broken and sieved to 10–20 meshgranules for reactor evaluation.

Example 15

To a 45 mL Parr Acid Digestion Bomb with an inner tube made of PTFE,0.53 g of tellurium dioxide (Aldrich), 0.2 mL of SeO₂ in water (Aldrich,0.1 M) and 20 mL of ammonium heptamolybdate tetrahydrate in water(Aldrich, 1.0 M in Mo) were added, and then 10 mL of vanadyl sulfatehydrate in water (Aldrich, 1.0 M in V) was added dropwise at ambienttemperature with stirring. The mixed suspension was hydrothermallytreated at 175° C. for 20 hours. Black solids formed on the wall andbottom of the bomb were collected by gravity filtration, washed withdeionized water (50 mL), dried in a vacuum oven at 25° C. overnight, andthen calcined in air from 25 to 275° C. at 10° C./min and held at 275°C. for 1 hour, then in Ar from 275 to 600° C. at 2° C./min and held at600° C. for 2 hours. The final catalyst had a nominal composition ofSe_(0.001)MoV_(0.5)Te_(0.17)O_(x). The catalyst thus obtained waspressed in a mold and then broken and sieved to 10–20 mesh granules forreactor evaluation.

Example 16

To a 100 mL Pyrex beaker, 1.06 g of tellurium dioxide (Aldrich) and 20mL of ammonium heptamolybdate tetrahydrate in water (Aldrich, 1.0 M inMo) were added. The mixture was heated on a hot plate at 80–100° C. for5 min., then 6.7 mL of vanadyl sulfate hydrate in water (Aldrich, 1.0 Min V) were added and the mixture was heated for another 5 min. at thesame temperature. The beaker contents were transferred to a 45 mL ParrAcid Digestion Bomb with an inner tube made of PTFE and washydrothermally treated at 175° C. for 20 hours. Black solids formed onthe wall and bottom of the bomb were collected by gravity filtration,washed with deionized water (50 mL), dried in a vacuum oven at 25° C.overnight, and then calcined in air from 25 to 300° C. at 3° C./min andheld at 300° C. for 1 hour in air and 1 hour in Ar, then heated in Arfrom 300 to 575° C. at 10° C./min and held at 575° C. for 2 hours. Thefinal catalyst had a nominal composition of MoV_(0.33)Te_(0.33)O_(x).The catalyst thus obtained was pressed in a mold and then broken andsieved to 10–20 mesh granules for reactor evaluation.

Example 17

To a 45 mL Parr Acid Digestion Bomb with an inner tube made of PTFE,1.06 g of tellurium dioxide (Aldrich) and 20 mL of ammoniumheptamolybdate tetrahydrate in water (Aldrich, 1.0 M in Mo) were added.The mixture was first hydrothermally treated at 150° C. for 1 hr, andthen 6.7 mL of vanadyl sulfate hydrate in water (Aldrich, 1.0 M in V)were added to the bomb at 60° C. with stirring. The bomb contents werehydrothermally treated at 175° C. for 60 hours. Black solids formed onthe wall and bottom of the bomb were collected by gravity filtration,washed with deionized water (50 mL), dried in a vacuum oven at 25° C.overnight, and then calcined in air from 25 to 275° C. at 10° C./min andheld at 275° C. for 1 hour, then in Ar from 275 to 575° C. at 2° C./minand held at 575° C. for 2 hours. The final catalyst had a nominalcomposition of MoV_(0.33)Te_(0.33)O_(x). The catalyst thus obtained waspressed in a mold and then broken and sieved to 10–20 mesh granules forreactor evaluation.

Example 18

To a 45 mL Parr Acid Digestion Bomb with an inner tube made of PTFE,1.06 g of tellurium dioxide (Aldrich) and 20 mL of ammoniumheptamolybdate tetrahydrate in water (Aldrich, 1.0 M in Mo) were added.The mixture was first hydrothermally treated at 100° C. for 1 hr, andthen 10 mL of vanadyl sulfate hydrate in water (Aldrich, 1.0 M in V)were added to the bomb at 60° C. with stirring. The bomb contents werehydrothermally treated at 175° C. for 20 hours. Black solids formed onthe wall and bottom of the bomb were collected by gravity filtration,washed with deionized water (50 mL), dried in a vacuum oven at 25° C.overnight, and then calcined in air from 25 to 300° C. at 3° C./min andheld at 300° C. for 1 hour in air and 1 hour in Ar, then heated in Arfrom 300 to 575° C. at 10° C./min and held at 575° C. for 2 hours. Thefinal catalyst had a nominal composition of MoV_(0.5)Te_(0.33)O_(x). Thecatalyst thus obtained was pressed in a mold and then broken and sievedto 10–20 mesh granules for reactor evaluation.

Example 19

To a 45 mL Parr Acid Digestion Bomb with an inner tube made of PTFE,1.59 g of tellurium dioxide (Aldrich) and 20 mL of ammoniumheptamolybdate tetrahydrate in water (Aldrich, 1.0 M in Mo) were added.The mixture was first hydrothermally treated at 100° C. for 1 hr, andthen 10 mL of vanadyl sulfate hydrate in water (Aldrich, 1.0 M in V)were added to the bomb at 60° C. with stirring. The bomb contents werehydrothermally treated at 175° C. for 60 hours. Black solids formed onthe wall and bottom of the bomb were collected by gravity filtration,washed with deionized water (50 mL), dried in a vacuum oven at 25° C.overnight, and then calcined in air from 25 to 275° C. at 10° C./min andheld at 275° C. for 1 hour, then in Ar from 275 to 575° C. at 2° C./minand held at 575° C. for 2 hours. The final catalyst had a nominalcomposition of MoV_(0.5)Te_(0.5)O_(x). The catalyst thus obtained waspressed in a mold and then broken and sieved to 10–20 mesh granules forreactor evaluation.

Example 20

To a 45 mL Parr Acid Digestion Bomb with an inner tube made of PTFE,1.03 g of tellurium dioxide (Aldrich), 20 mL of ammonium heptamolybdatetetrahydrate in water (Aldrich, 1.0 M in Mo) and 1 mL of aqueous MoCl₅(Aldrich, 0.1 M in Cl) were added. The mixture was first hydrothermallytreated at 100° C. for 1 hr, and then 10 mL of vanadyl sulfate hydratein water (Aldrich, 1.0 M in V) were added to the bomb at 60° C. withstirring. The bomb contents were hydrothermally treated at 175° C. for20 hours. Black solids formed on the wall and bottom of the bomb werecollected by gravity filtration, washed with deionized water (50 mL),dried in a vacuum oven at 25° C. overnight, and then calcined in airfrom 25 to 300° C. at 3° C./min and held at 300° C. for 1 hour in airand 1 hour in Ar, then heated in Ar from 300 to 575° C. at 10° C./minand held at 575° C. for 2 hours. The final catalyst had a nominalcomposition of Cl_(0.025)MoV_(0.05)Te_(0.33)O_(x). The catalyst thusobtained was pressed in a mold and then broken and sieved to 10–20 meshgranules for reactor evaluation.

Example 21

To a 45 mL Parr Acid Digestion Bomb with an inner tube made of PTFE,1.03 g of tellurium dioxide (Aldrich), 20 mL of ammonium heptamolybdatetetrahydrate in water (Aldrich, 1.0 M in Mo) and 1 mL of H₅As₃O₁₀ inwater (Aldrich, 0.1 M in As) were added. The mixture was firsthydrothermally treated at 80° C. for 1 hr, and then 10 mL of vanadylsulfate hydrate in water (Aldrich, 1.0 M in V) were added to the bomb at60° C. with stirring. The bomb contents were hydrothermally treated at175° C. for 20 hours. Black solids formed on the wall and bottom of thebomb were collected by gravity filtration, washed with deionized water(50 mL), dried in a vacuum oven at 25° C. overnight, and then calcinedin air from 25 to 275° C. at 10° C./min and held at 275° C. for 1 hour,then in Ar from 275 to 600° C. at 2° C./min and held at 600° C. for 2hours. The final catalyst had a nominal composition ofAs_(0.025)MoV_(0.5)Te_(0.33)O_(x). The catalyst thus obtained waspressed in a mold and then broken and sieved to 10–20 mesh granules forreactor evaluation.

Example 22

To a 100 mL Pyrex beaker, 1.06 g of tellurium dioxide (Aldrich), 20 mLof ammonium heptamolybdate tetrahydrate in water (Aldrich, 1.0 M in Mo)and 1 mL of H₅As₃O₁₀ in water (Aldrich, 0.1 M in As) were added. Themixture was heated on a hot plate at 80–100° C. for 5 min., then 10 mLof vanadyl sulfate hydrate in water (Aldrich, 1.0 M in V) were added andthe mixture was heated for another 5 min. at the same temperature. Thebeaker contents were transferred to a 45 mL Parr Acid Digestion Bombwith an inner tube made of PTFE and was hydrothermally treated at 175°C. for 20 hours. Black solids formed on the wall and bottom of the bombwere collected by gravity filtration, washed with deionized water (50mL), dried in a vacuum oven at 25° C. overnight, and then calcined inair from 25 to 275° C. at 10° C./min and held at 275° C. for 1 hour,then in Ar from 275 to 575° C. at 2° C./min and held at 575° C. for 2hours. The final catalyst had a nominal composition ofAs_(0.025)MoV_(0.5)Te_(0.33)O_(x). The catalyst thus obtained waspressed in a mold and then broken and sieved to 10–20 mesh granules forreactor evaluation.

Example 23

To a 100 mL Pyrex beaker, 1.06 g of tellurium dioxide (Aldrich), 20 mLof ammonium heptamolybdate tetrahydrate in water (Aldrich, 1.0 M in Mo)and 1 mL of Pb(NO₃)₂ in water (Aldrich, 0.1 M) were added. The slurrywas heated on a hot plate at 80–100° C. for 5 min., then 10 mL ofvanadyl sulfate hydrate in water (Aldrich, 1.0 M in V) were added andthe mixture was heated for another 5 min. at the same temperature. Thebeaker contents were transferred to a 45 mL Parr Acid Digestion Bombwith an inner tube made of PTFE and was hydrothermally treated at 175°C. for 20 hours. Black solids formed on the wall and bottom of the bombwere collected by gravity filtration, washed with deionized water (50mL), dried in a vacuum oven at 25° C. overnight, and then calcined inair from 25 to 300° C. at 3° C./min and held at 300° C. for 1 hour inair and 1 hour in Ar, then heated in Ar from 300 to 575° C. at 10°C./min and held at 575° C. for 2 hours. The final catalyst had a nominalcomposition of Pb_(0.25)MoV_(0.5)Te_(0.33)O_(x). The catalyst thusobtained was pressed in a mold and then broken and sieved to 10–20 meshgranules for reactor evaluation.

Example 24

To a 100 mL Pyrex beaker, 1.06 g of tellurium dioxide (Aldrich), 20 mLof ammonium heptamolybdate tetrahydrate in water (Aldrich, 1.0 M in Mo)and 0.2 mL of Au(OH)₃ in water (Aldrich, 0.1 M) were added. The mixturewas heated on a hot plate at 80–100° C. for 5 min., then 10 mL ofvanadyl sulfate hydrate in water (Aldrich, 1.0 M in V) were added andthe mixture was heated for another 5 min. at the same temperature. Thebeaker contents were transferred to a 45 mL Parr Acid Digestion Bombwith an inner tube made of PTFE and was hydrothermally treated at 175°C. for 20 hours. Black solids formed on the wall and bottom of the bombwere collected by gravity filtration, washed with deionized water (50mL), dried in a vacuum oven at 25° C. overnight, and then calcined inair from 25 to 300° C. at 3° C./min and held at 300° C. for 1 hour inair and 1 hour in Ar, then heated in Ar from 300 to 575° C. at 10°C./min and held at 575° C. for 2 hours. The final catalyst had a nominalcomposition of Au_(0.025)MoV_(0.5)Te_(0.33)O_(x). The catalyst thusobtained was pressed in a mold and then broken and sieved to 10–20 meshgranules for reactor evaluation.

Comparative Example 2

To a 45 mL Parr Acid Digestion Bomb with an inner tube made of PTFE,0.93 g of Sb₂(SO₄)₃ (Aldrich) and 21 mL of ammonium heptamolybdatetetrahydrate in water (Aldrich, 1.0 M in Mo) were added. The mixture wasfirst hydrothermally treated at 150° C. for 30 min., and then 7 mL ofvanadyl sulfate hydrate in water (Aldrich, 1.0 M in V) were added to thebomb at 80° C. with stirring. The bomb contents were hydrothermallytreated at 175° C. for 20 hours. Black solids formed on the wall andbottom of the bomb were collected by gravity filtration, washed withdeionized water (50 mL), dried in a vacuum oven at 25° C. overnight, andthen calcined in air from 25 to 300° C. at 3° C./min and held at 300° C.for 1 hour in air and 1 hour in Ar, then heated in Ar from 300 to 575°C. at 10° C./min and held at 575° C. for 2 hours. The final catalyst hada nominal composition of MoV_(0.33)Sb_(0.17)O_(x). The catalyst thusobtained was pressed in a mold and then broken and sieved to 10–20 meshgranules for reactor evaluation.

Comparative Example 3

To a 100 mL Pyrex beaker, 1.06 g of Sb₂(SO₄)₃ (Aldrich) and 24 mL ofammonium heptamolybdate tetrahydrate in water (Aldrich, 1.0 M in Mo)were added. The mixture was heated on a hot plate at 80–100° C. for 5min., then 8 mL of vanadyl sulfate hydrate in water (Aldrich, 1.0 M inV) were added and the mixture was heated for another 5 min. at the sametemperature. The beaker contents were transferred to a 45 mL Parr AcidDigestion Bomb with an inner tube made of PTFE and was hydrothermallytreated at 175° C. for 20 hours. Black solids formed on the wall andbottom of the bomb were collected by gravity filtration, washed withdeionized water (50 mL), dried in a vacuum oven at 25° C. overnight, andthen calcined in air from 25 to 275° C. at 0° C./min and held at 275° C.for 1 hour, then in Ar from 275 to 575° C. at 2° C./min and held at 575°C. for 2 hours. The final catalyst had a nominal composition ofMoV_(0.33)Sb_(0.17)O_(x). The catalyst thus obtained was pressed in amold and then broken and sieved to 10–20 mesh granules for reactorevaluation.

Example 25

To a 100 mL Pyrex beaker, 0.93 g of Sb₂(SO₄)₃ (Aldrich), 21 mL ofammonium heptamolybdate tetrahydrate in water (Aldrich, 1.0 M in Mo) and1 mL of VF₃ in water (Aldrich, 0.1 M in F) were added. The mixture washeated on a hot plate at 80–100° C. for 5 min., then 7 mL of vanadylsulfate hydrate in water (Aldrich, 1.0 M in V) were added and themixture was heated for another 5 min. at the same temperature. Thebeaker contents were transferred to a 45 mL Parr Acid Digestion Bombwith an inner tube made of PTFE and was hydrothermally treated at 175°C. for 20 hours. Black solids formed on the wall and bottom of the bombwere collected by gravity filtration, washed with deionized water (50mL), dried in a vacuum oven at 25° C. overnight, and then calcined inair from 25 to 275° C. at 10° C./min and held at 275° C. for 1 hour,then in Ar from 275 to 575° C. at 2° C./min and held at 575° C. for 2hours. The final catalyst had a nominal composition ofF_(0.025)MoV_(0.33)Sb_(0.17)O_(x). The catalyst thus obtained waspressed in a mold and then broken and sieved to 10–20 mesh granules forreactor evaluation.

Example 26

To a 100 mL Pyrex beaker, 0.93 g of Sb₂(SO₄)₃ (Aldrich), 21 mL ofammonium heptamolybdate tetrahydrate in water (Aldrich, 1.0 M in Mo) and1 mL of Au(OH)₃ in water (Aldrich, 0.1 M) were added. The mixture washeated on a hot plate at 80–100° C. for 5 min., then 10 mL of vanadylsulfate hydrate in water (Aldrich, 1.0 M in V) were added and themixture was heated for another 5 min. at the same temperature. Thebeaker contents were transferred to a 45 mL Parr Acid Digestion Bombwith an inner tube made of PTFE and was hydrothermally treated at 175°C. for 20 hours. Black solids formed on the wall and bottom of the bombwere collected by gravity filtration, washed with deionized water (50mL), dried in a vacuum oven at 25° C. overnight, and then calcined inair from 25 to 275° C. at 10° C./min and held at 275° C. for 1 hour,then in Ar from 275 to 575° C. at 2° C./min and held at 575° C. for 2hours. The final catalyst had a nominal composition ofAu_(0.025)MoV_(0.33)Sb_(0.17)O_(x). The catalyst thus obtained waspressed in a mold and then broken and sieved to 10–20 mesh granules forreactor evaluation.

EVALUATION AND RESULTS

Catalysts were evaluated in a 10 cm long Pyrex tube reactor (internaldiameter: 3.9 mm). The catalyst bed (4 cm long) was positioned withglass wool at approximately mid-length in the reactor and was heatedwith an electric furnace. Mass flow controllers and meters regulated thegas flow rate. The oxidation was conducted using a feed gas stream ofpropane, steam and air, with a feed ratio of propane:steam:air of1:3:96. The reactor effluent was analyzed by a FTIR. The results at a 3second residence time are shown in Tables 1–4.

TABLE 1 Temp. % C3 Catalyst Composition ° C. Conv. % AA yield Comp. Ex.1 MoV_(0.5)Te_(0.17)O_(x) 393 27 2 Ex. 1Ga_(0.025)MoV_(0.5)Te_(0.17)O_(x) 372 35 6 Ex. 2Br_(0.005)MoV_(0.5)Te_(0.17)O_(x) 402 51 7 Ex. 3F_(0.005)MoV_(0.5)Te_(0.17)O_(x) 284 29 12 Ex. 4Bi_(0.005)MoV_(0.5)Te_(0.17)O_(x) 366 23 5 Ex. 5I_(0.005)MoV_(0.5)Te_(0.17)O_(x) 376 25 7 Ex. 6Ge_(0.005)MoV_(0.5)Te_(0.17)O_(x) 366 36 11 Ex. 7La_(0.025)MoV_(0.5)Te_(0.17)O_(x) 384 42 8 Ex. 8Y_(0.005)MoV_(0.5)Te_(0.17)O_(x) 385 42 11 Ex. 9Y_(0.005)MoV_(0.5)Te_(0.33)O_(x) 385 40 13 Ex. 10Ag_(0.025)MoV_(0.5)Te_(0.17)O_(x) 403 24 4 Ex. 11Zn_(0.005)MoV_(0.5)Te_(0.17)O_(x) 393 39 6 Ex. 12Au_(0.001)MoV_(0.5)Te_(0.17)O_(x) 385 28 10 Ex. 13As_(0.005)MoV_(0.5)Te_(0.17)O_(x) 393 56 9 Ex. 14Pb_(0.005)MoV_(0.5)Te_(0.17)O_(x) 384 36 12 Ex. 15Se_(0.001)MoV_(0.5)Te_(0.17)O_(x) 403 27 3

TABLE 2 Catalyst Composition Temp. ° C. % C3 Conv. % AA yield Ex. 16MoV_(0.33)Te_(0.33)O_(x) 368 56 27 Ex. 16 MoV_(0.33)Te_(0.33)O_(x) 40078 20 Ex. 17 MoV_(0.33)Te_(0.33)O_(x) 394 52 29 Ex. 18MoV_(0.5)Te_(0.33)O_(x) 396 56 30 Ex. 19 MoV_(0.5)Te_(0.5)O_(x) 381 5031

TABLE 3 Temp. Catalyst Composition ° C. % C3 Conv. % AA yield Ex. 20Cl_(0.025)MoV_(0.5)Te_(0.33)O_(x) 357 65 26 Ex. 21As_(0.025)MoV_(0.5)Te_(0.33)O_(x) 390 44 25 Ex. 22As_(0.025)MoV_(0.5)Te_(0.33)O_(x) 369 48 21 Ex. 23Pb_(0.025)MoV_(0.5)Te_(0.33)O_(x) 369 34 21 Ex. 24Au_(0.025)MoV_(0.5)Te_(0.33)O_(x) 387 29 14

TABLE 4 Temp. % C3 Catalyst Composition ° C. Conv. % AA yield Comp. Ex.2 MoV_(0.33)Sb_(0.17)O_(x) 402 97 6 Comp. Ex. 3 MoV_(0.33)Sb_(0.17)O_(x)393 64 1 Ex. 25 F_(0.025)MoV_(0.33)Sb_(0.17)O_(x) 260 21 8 Ex. 26Au_(0.025)MoV_(0.33)Sb_(0.17)O_(x) 241 13 8

1. A process for producing an unsaturated carboxylic acid whichcomprises subjecting an alkane, or a mixture of an alkane and an alkene,to a vapor phase catalytic oxidation reaction in the presence of acatalyst comprising a mixed metal oxide having the empirical formulaMo_(a)V_(b)M_(c)X_(d)O_(e) wherein M is an element selected from thegroup consisting of Te, Sb and Nb, wherein X is an element selected fromthe group consisting of Sc, Y, La, Re, Ir, Cu, Ag, Au, Zn, Ga, Si, Ge,As, Pb, S, Se, Sn, Bi, F, Cl, Br and I, and wherein, when a=1, b=0.01 to1.0, c=0.01 to 1.0, d=0 to 1 and e is dependent on the oxidation stateof the other elements; with the proviso that, when d=0, M is selectedfrom the group consisting of Nb and Te, and with the further provisothat, when d=0 and M=Te, 0.01≦b<0.50 or 0.17<c≦1.0.
 2. The process forproducing an unsaturated carboxylic acid according to claim 1, whereinsaid catalyst is produced by a synthesis process comprising: (i)admixing compounds of elements Mo, V, M and X, as needed, and a solventcomprising water to form a first admixture containing at least 2 butless than all of said elements Mo, V, M and X; (ii) heating said firstadmixture at a temperature of from 80° C. to 150° C. for from 5 minutesto 48 hours; (iii) then, admixing compounds of elements Mo, V, M and X,as needed, with said first admixture to form a second admixturecontaining elements Mo, V, M and X, in the respective atomic proportionsa, b, c and d, wherein, when a=1, b=0.01 to 1.0, c=0.01 to 1.0 and d=0to 1; (iv) heating said second admixture at a temperature of from 50° C.to 300° C. for from 1 hour to several weeks, in a closed vessel underpressure; (v) recovering insoluble material from said closed vessel toobtain a catalyst.
 3. The process for producing an unsaturatedcarboxylic acid according to claim 2, wherein said synthesis processfurther comprises calcining said recovered insoluble material.
 4. Theprocess for producing an unsaturated carboxylic acid according to claim3, wherein said calcination comprises heating said recovered insolublematerial to a first temperature in an oxidizing atmosphere, then heatingthe so-treated recovered insoluble material from said first temperatureto a second temperature in a non-oxidizing atmosphere.
 5. The processfor producing an unsaturated carboxylic acid according to claim 2,wherein said first admixture comprises the elements Mo, M and X.
 6. Theprocess for producing an unsaturated carboxylic acid according to claim5, wherein M=Te.